1. Field of the Invention
The present invention relates to a manufacturing method of a lead frame for an optical coupling device (e.g., photocoupler) that is suitably used for an electronic apparatus such as, in particular, a television and a mobile telephone; a lead frame manufactured by this method; and a manufacturing method of an optical coupling device using this lead frame.
2. Description of the Related Art
FIG. 1 shows a structure of a conventional optical coupling device, and FIG. 2 shows a lead frame to be used in the optical coupling device. The optical coupling device is manufactured by using this lead frame as follows.
A light-emitting element (1) and a light-receiving element (2) are respectively die-bonded (bonded) to a lead frame A (3) that is provided with a header on which an element is mounted and another lead frame B (3′) individually. Further, wire-bonding processes in which the light-emitting element (1) and the light-receiving element (2) are connected to external leads through gold wires (4) are respectively carried out thereon, and the light-emitting element (1) is then subjected to a coating process by using a silicone resin (5) so as to alleviate stress.
Then, the two lead frames A (3) and B (3′) are placed face to face with each other so as to make the optical axes of the light-emitting element (1) and the light-receiving element (2) coincident with each other. This is then subjected to a primary molding process by using a light-transmitting epoxy resin (6), and the entire portion of this that has been subjected to the primary molding process is then subjected to a transfer-molding process by using a light-shielding epoxy resin (7), that is, a secondary molding process.
The resulting product is then subjected to respective processes, such as an external plating process, a lead-forming process (external lead machining process), an insulation voltage-resistant test (insulation property test between the primary mold and the secondary mold), an electric characteristic test (measurements on various electric characteristics), a marking process, an appearance test and a packaging process; thus, a finished product is prepared.
With respect to the means for molding processes, in addition to the above-mentioned transfer-molding process, processes, such as an injection molding process and a casting process, may be used.
Moreover, as shown in FIG. 3, in the above-mentioned primary molding process, another method in which, instead of the light-transmitting epoxy resin (6), a transparent silicone resin (8) is used for forming a path between the light-emitting element (1) and the light-receiving element (2) may be used.
Examples of the prior-art techniques relating to the lead frame for optical coupling devices are disclosed in JP-A Hei 06(1994)-237010, JP-A Hei 06(1994)-350128 and JP-A Hei 06(1994)-132561.
FIG. 4 shows a manufacturing flowchart and a line block diagram of a conventional optical coupling device, which include processes from die-bonding processes of light-emitting elements and light-receiving elements, through an overlapping process, a primary molding process, a secondary molding process, an external plating process and a lead forming process, to a packing process for a finished product.
Moreover, FIG. 5 shows a manufacturing method of a conventional lead frame.
First, a metal material (Cu material, Fe material or the like), wound into a coil, is prepared, and this is stamped by using a stamping metal mold so that an element mounting header is formed. Further, the header portion and the wire-bond 2nd portion are subjected to a plating process, and the header portion is then bent over, and cut out into straps with a specified length.
In general, the manufacturing processes are carried out in the above-mentioned sequence; however, after the plating process has been first carried out, the processes such as stamping, bending and strap-shape cutting processes may be then carried out, or the processes such as stamping, bending, plating and strap-shape cutting processes may be carried out in this order.
Upon using the lead frame obtained as described above, a lead frame on which a light-emitting element is mounted and a lead frame on which a light-receiving element is mounted are required, and since these elements need to be die-bonded and wire-bonded respectively, independent transport systems are respectively required on the light-emitting element side as well as on the light-receiving element side (see line structural diagram of FIG. 4).
For this reason, a wide installation space is required in the manufacturing line, causing high costs of equipment. Moreover, with respect to the lead frame manufacturing processes, since two lead frames are required on the light-emitting element side as well as on the light-receiving element side, two dies (trimming dies) used for manufacturing the lead frames are required, resulting in high lead frame manufacturing costs as well as high material and die costs.
In recent years, the price competition of electronic components has been intensified, and in response to this circumstance, it is indispensable to reduce fixed costs such as equipment service costs in addition to variable costs such as material costs. Further, proposed countermeasures are material use with high efficiency (reduction of material costs per one electronic component), reduction in facility costs by improvements in the facility and reduction in facility costs by simplifying the facility structure.
Recently, a plane mounted optical coupling element in which light-emitting elements and light-receiving elements are integrally formed into one piece and flatly mounted on the lead frame has also been developed.
However, although such a plane mounted optical coupling element has advantages in that the lead frame price and costs required for transport-system facilities are reduced, it has a structure that tends to cause a lead deformation upon cutting a lead frame due to limitations in the manufacturing process.